Before writing to a heat-assisted magnetic recording medium, a current of a laser is modulated about a default threshold current level. A modulation level of an optical power sensor is measured, the optical power sensor being coupled to detect optical output of the laser in response to the modulated current. A bias current for subsequent activation of the laser is adjusted based on the modulation level of the optical power sensor.
Legal claims defining the scope of protection. Each claim is shown in both the original legal language and a plain English translation.
1. A method, comprising: before writing to a heat-assisted magnetic recording medium via a laser of a read/write head, modulating a DC current of the laser about a default DC level; measuring a modulation level of an optical power sensor that is coupled to detect optical output of the laser in response to the modulated current; and adjusting a bias current for subsequent activation of the laser based on the modulation level of the optical power sensor.
Before writing data to a heat-assisted magnetic recording medium, a laser's DC current is modulated around a default DC level. An optical power sensor, which detects the laser's optical output in response to the modulated current, measures the modulation level. The bias current used to subsequently activate the laser is then adjusted based on this measured modulation level of the optical power sensor. This allows for precise control of the laser power before writing.
2. The method of claim 1 , further comprising using the adjusted bias current for subsequent write operations.
The method from the previous description, where a laser's DC current is modulated around a default DC level before writing data to a heat-assisted magnetic recording medium, an optical power sensor measures the modulation level, and a bias current is adjusted, goes on to use the adjusted bias current for subsequent write operations on the magnetic medium.
3. The method of claim 2 , wherein using the adjusted bias current for the subsequent write operations comprises adding an operational current to the adjusted bias current to fully activate the laser.
The method from the previous description, where a laser's DC current is modulated around a default DC level before writing data to a heat-assisted magnetic recording medium, an optical power sensor measures the modulation level, a bias current is adjusted, and the adjusted bias current is used for subsequent write operations, fully activates the laser by adding an operational current to the adjusted bias current. The operational current provides the additional power needed for writing after the bias current has been optimized.
4. The method of claim 3 , further comprising: determining a slope efficiency based on the modulation level of the optical power sensor; and modifying the operational current based on the slope efficiency.
The method from the previous descriptions, where a laser's DC current is modulated around a default DC level before writing data to a heat-assisted magnetic recording medium, an optical power sensor measures the modulation level, a bias current is adjusted, the adjusted bias current is used for subsequent write operations, and the laser is fully activated, further determines a slope efficiency based on the modulation level of the optical power sensor and modifies the operational current based on this slope efficiency. This optimizes laser power usage during writing.
5. The method of claim 1 , wherein the modulation level of the optical power sensor as a function of the modulated current is an s-shaped curve asymptotically approaching zero as the modulated current becomes small enough not to activate the laser and approaching an output level A as the modulated current becomes large enough to continuously activate the laser.
This invention relates to optical power sensing in laser systems, specifically addressing the challenge of accurately measuring optical power output in response to modulated drive currents. The method involves using an optical power sensor to detect the laser's output, where the sensor's modulation level exhibits an S-shaped response curve. This curve asymptotically approaches zero when the modulated current is too low to activate the laser and reaches a stable output level A when the current is sufficient to continuously activate the laser. The S-shaped characteristic ensures that the sensor provides a clear, distinguishable signal transition between the laser's inactive and active states, improving measurement accuracy. The method may also include adjusting the sensor's sensitivity or calibration to account for variations in the laser's threshold current or other operational parameters. This approach enhances the reliability of optical power monitoring in systems where the laser's activation state changes dynamically, such as in pulsed or modulated laser applications. The sensor's response curve is designed to minimize ambiguity in power measurements, particularly at low modulation currents where traditional sensors may produce unreliable or noisy signals. The invention is applicable in telecommunications, industrial laser systems, and other fields requiring precise optical power control.
6. The method of claim 5 , wherein the adjusting the bias current based on the modulated level of the optical power sensor comprises adjusting the bias current so that the modulation level of the optical power sensor is a target value between A/4 and 3A/4.
In the method using the S-shaped curve of the optical power sensor, where the sensor's modulation level approaches zero when the laser is off and "A" when fully on, adjusting the bias current involves setting it so the sensor's modulation level falls between A/4 and 3A/4. This target range optimizes the bias current to achieve the desired laser output power efficiently.
7. The method of claim 1 , wherein the optical power sensor detects the optical output of the laser based on detecting a temperature proximate a light delivery path of the read/write head.
In the method where a laser's DC current is modulated, the optical power sensor detects the laser's output by measuring the temperature near the read/write head's light delivery path. This temperature-based detection provides feedback on the laser's performance, allowing for precise adjustments to be made.
8. The method of claim 1 , wherein modulating the current of the laser comprises a sinusoidal modulation of the DC current, the default DC level comprising a previously determined threshold current of the laser.
In the method where a laser's DC current is modulated, the modulation involves a sinusoidal change to the DC current around a default DC level. This default DC level is a previously determined threshold current for the laser. Using a sinusoidal modulation around the threshold improves laser control.
9. The method of claim 8 , wherein a peak-to-peak amplitude of the sinusoidal modulation depends on a magnitude of the DC current.
In the method using sinusoidal modulation of the laser current around a default threshold, the peak-to-peak amplitude of the sinusoidal modulation depends on the magnitude of the DC current. Adjusting the amplitude based on the DC current enhances the accuracy and effectiveness of the modulation process.
10. The method of claim 1 , wherein the method is performed during an adjacent track seek that occurs before writing to the heat-assisted magnetic recording medium.
The method where a laser's DC current is modulated occurs during an adjacent track seek before writing data to the heat-assisted magnetic recording medium. Performing the modulation and adjustment during the seek optimizes performance without impacting write speeds.
11. An apparatus comprising: circuitry that interfaces with a laser of a read/write head, the laser using in writing data to a heat-assisted magnetic recording medium; and a controller coupled to the circuitry and configured to perform a procedure comprising: modulate a current of the laser about one or more DC current levels selected to at least partially activate the laser; in response to the modulated current, measure at least one modulation level of an optical power sensor that is coupled to detect optical output of the laser; and based on the modulation level of the optical power sensor, adjust at least one of a bias current for subsequent activation of the laser and an operational current added to the bias current during writing.
An apparatus for controlling a laser used in heat-assisted magnetic recording includes circuitry interfacing with the laser, and a controller. The controller modulates the laser current around one or more DC levels that at least partially activates the laser. In response, the controller measures the modulation level of an optical power sensor coupled to the laser. Based on this modulation level, it adjusts either a bias current for subsequent laser activation or an operational current added to the bias current during writing, or both. This allows fine tuning of the laser.
12. The apparatus of claim 11 , wherein the controller is configured to adjust the bias current and is further configured to add the operational current to the adjusted bias current to fully activate the laser for subsequent write operations.
The apparatus from the previous description, which includes circuitry interfacing with the laser, and a controller that modulates the laser current, measures the modulation level of an optical power sensor, and adjusts a bias current, further configures the controller to add an operational current to the adjusted bias current to fully activate the laser for subsequent write operations. This provides both a baseline and the required power for writing.
13. The apparatus of claim 12 , wherein the controller is configured determine the slope efficiency and to modify the operational current based on the slope efficiency.
The apparatus from the previous description, which includes circuitry interfacing with the laser, and a controller that modulates the laser current, measures the modulation level of an optical power sensor, adjusts a bias current, and adds an operational current, further has the controller determine the laser's slope efficiency and modifies the operational current based on this slope efficiency. This achieves optimal laser power during the writing process.
14. The apparatus of claim 11 , wherein the modulation level of the optical power sensor as a function of the modulated current is an s-shaped curve asymptotically approaching zero as the modulated current becomes small enough not to activate the laser and approaching an output level A as the modulated current becomes large enough to continuously activate the laser.
In the apparatus where a laser's current is modulated, the relationship between the optical power sensor's modulation level and the modulated current follows an S-shaped curve. The curve asymptotically approaches zero as the modulated current becomes too small to activate the laser. Conversely, it approaches an output level "A" as the current becomes large enough to continuously activate the laser. This characteristic curve allows for accurate laser control.
15. The apparatus of claim 14 , wherein the adjusting of the bias current comprises adjusting the bias current so that the modulation level of the optical power sensor is a target value between A/4 and 3A/4.
In the apparatus using the S-shaped curve of the optical power sensor, where the sensor's modulation level approaches zero when the laser is off and "A" when fully on, the bias current is adjusted so the sensor's modulation level falls between A/4 and 3A/4. This target range optimizes the bias current to achieve the desired laser output power efficiently.
16. The apparatus of claim 11 , wherein the optical power sensor comprises a bolometer.
In the apparatus for controlling a laser, the optical power sensor is a bolometer. This sensor type allows for precise measurement of the laser's optical output by detecting heat.
17. The apparatus of claim 16 , wherein the controller is configured to adjust the bias current, and wherein the one or more DC current levels comprises a previously determined default threshold current level of the laser.
In the apparatus that uses a bolometer as an optical power sensor and adjusts the laser bias current, the DC current level used for modulation comprises a previously determined default threshold current level of the laser.
18. A method comprising: applying at least two different modulated DC currents to a laser used in writing data to a heat-assisted magnetic recording medium; measuring first and second modulation levels of an optical power sensor that is coupled to detect an optical output of the laser in response to the at least two modulated DC currents, the first and second modulation levels respectively corresponding to a first of the modulated DC currents that causes the laser to begin emitting light and a second of the modulated DC currents that is large enough to continuously activate the laser; and determining a slope efficiency of the laser based on the first and second modulated DC currents.
A method involves applying at least two different modulated DC currents to a laser used for heat-assisted magnetic recording. First and second modulation levels are measured using an optical power sensor, where the levels respectively correspond to a first modulated DC current that causes the laser to begin emitting light and a second current that is large enough to continuously activate the laser. A slope efficiency of the laser is determined based on these two modulated DC currents.
19. The method of claim 18 , further comprising setting a laser operational current based on the slope efficiency.
The method from the previous description, where at least two modulated DC currents are applied to a laser, first and second modulation levels are measured, and a slope efficiency is determined, goes on to set the laser operational current based on the determined slope efficiency.
20. The method of claim 18 , wherein applying the at least two different modulated DC currents comprises applying a series of currents in the form of I dc +B cos(ωt) for different values of I dc , where B and ω are constant.
The method from the previous descriptions, where at least two modulated DC currents are applied to a laser, first and second modulation levels are measured, and a slope efficiency is determined, applies a series of currents in the form Idc + B*cos(ωt) for different values of Idc, where B and ω are constant.
Cooperative Patent Classification codes for this invention. Click any code to explore related patents in that topic.
October 25, 2016
August 22, 2017
Browse 5M+ US patents with plain-English claim translations and AI-generated analysis.